1. Field of the Invention
This invention relates to organosilicon compounds exhibiting properties characteristic of liquid crystals. This invention further relates to liquid crystalline organosilicon compounds exhibiting rapidly reversible liquid crystal phase transitions over a wide and relatively low temperature range.
2. Background Information
Many organic compounds exhibit a liquid crystal phase over a particular temperature range. In addition, numerous polymeric organic compounds with a liquid crystal (mesogenic) group in the main chain or side chain exhibit the same effect. There are, however, relatively few examples of polyorganosiloxanes having a liquid crystal phase.
Liquid crystalline polyorganosiloxanes are disclosed in U.S. Pat. No. 4,358,391, issued to Finkelmann et al. on Nov. 9, 1982, U.S. Pat. No. 4,388,453, issued to Finkelmann et al. on June 14, 1983, and U.S. Pat. No. 4,410,570, issued to Kreuzer et al. on Oct. 18, 1983. The polymers of U.S. Pat. No. 4,358,391 contain mesogenic groups bonded as side chains to a linear polydiorganosiloxane. The solid crystal-liquid crystal transition temperature exhibited by these polymers is considerably lower compared to other types of liquid crystalline polymers such as polyacrylic acid esters. In addition, the long period of time required to achieve the reversible transitions from solid crystal to liquid crystal to isotropic liquid makes these transitions substantially irreversible for all practical purposes. The delayed phase transitions may be due to a delay in orientation of the mesogenic group that in turn results from restrictions imposed by the structure of the polyorganosiloxane molecule.
The aforementioned U.S. Pat. No. 4,388,453 discloses three dimensional, crosslinked polyorganosiloxanes containing mesogenic groups within the polymer network. In addition to the disadvantages cited hereinabove in connection with U.S. Pat. No. 4,358,391, the degree of crosslinking must be carefully controlled during polymerization to achieve the required uniform liquid crystalline structure in the final product.
The aforementioned U.S. Pat. No. 4,410,570 teaches eliminating the disadvantage of a slow transition between crystalline and liquid phases that is characteristic of linear polydiorganosiloxanes by employing a cyclic polyorganosiloxane in place of the linear polymer, however this results in an increase in the solid crystal-liquid crystal-isotropic liquid transition temperatures to at least 100.degree. C. The high temperature required to achieve a liquid crystal transition more than outweighs any advantages associated with using polyorganosiloxanes as vehicles for bonding mesogenic groups.
U.S. Pat. No. 4,316,041 discloses silanes of the general formula ##STR1## where M is methoxy, ethoxy, chloro or dimethylamino, R' is hydrogen, methyl or ethyl; G is alkylene having from 2 to 4 carbon atoms or arylene of aralkylene, where the arylene and aralkylene radicals contain from 6 to 8 carbon atoms, E is --O-- or --NH--; Z is one of four different mesogenic groups; x is from 0 to 2 and y is from 1 to 3. The silanes are prepared by reacting an isocyanatohydrocarbyl-substituted silane with the appropriate mesogenic compound containing a hydroxyl or amino group as a substituent.
An objective of this invention is to provide non-crosslinked liquid crystalline organosilicon compounds that do not exhibit the disadvantages of prior art organosilicon materials.